Technical Abstract: Aflatoxins are extremely toxic and carcinogenic secondary metabolites produced primarily by the fungi Aspergillus flavus and A. parasiticus. In order to better understand the molecular mechanisms regulating aflatoxin biosynthesis, gene profiling through A. flavus expressed sequence tag (EST) and microarray have been carried out. A total of 7,218 unique EST sequences have been obtained from a normalized A. flavus cDNA library. Genes that are possibly related to aflatoxin formation have been identified from these ESTs. Results from gene profiling have showed that hundreds of genes were found to be expressed or up-regulated under aflatoxin-producing conditions. The results of this research are expected to provide information for developing new strategies for control of aflatoxin contamination of agricultural commodities.